Power control system for current regulated light sources

ABSTRACT

A light emitting diode (LED) lighting system includes a PFC and output voltage controller and a LED lighting power system. The controller advantageously operates from an auxiliary voltage less than a link voltage generated by the LED lighting power system. The common reference voltage allows all the components of lighting system to work together. A power factor correction switch and an LED drive current switch are coupled to the common reference node and have control node-to-common node, absolute voltage that allows the controller to control the conductivity of the switches. The LED lighting system can utilize feed forward control to concurrently modify power demand by the LED lighting power system and power demand of one or more LEDs. The LED lighting system can utilize a common current sense device to provide a common feedback signal to the controller representing current in at least two of the LEDs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending application Ser. No.12/858,004, filed Aug. 17, 2010, which claims the benefit of applicationSer. No. 12/047,262, filed Mar. 12, 2008, now U.S. Pat. No. 7,804,256,which claims the benefit of Application No. 60/894,295, filed Mar. 12,2007, and Application No. 60/909,458, filed Apr. 1, 2007, all of whichare incorporated herein by reference in their entireties.

U.S. patent application Ser. No. 12/047,249, entitled “Ballast for LightEmitting Diode Light Sources,” inventor John L. Melanson, and filed onMar. 12, 2008 describes exemplary methods and systems and isincorporated by reference in its entirety.

U.S. patent application Ser. No. 11/926,864, entitled “Color Variationsin a Dimmable Lighting Device with Stable Color Temperature LightSources,” inventor John L. Melanson, and filed on Mar. 31, 2007describes exemplary methods and systems and is incorporated by referencein its entirety.

U.S. Provisional Application No. 60/909,457, entitled “Multi-FunctionDuty Cycle Modifier,” inventors John L. Melanson and John Paulos, andfiled on Mar. 31, 2007 describes exemplary methods and systems and isincorporated by reference in its entirety. Referred to herein asMelanson I.

U.S. patent application Ser. No. 12/047,258, entitled “Multi-FunctionDuty Cycle Modifier,” inventors John L. Melanson and John Paulos, andfiled on Mar. 12, 2008 describes exemplary methods and systems and isincorporated by reference in its entirety. Referred to herein asMelanson II.

U.S. patent application Ser. No. 11/695,024, entitled “Lighting Systemwith Lighting Dimmer Output Mapping,” inventors John L. Melanson andJohn Paulos, and filed on Mar. 31, 2007 describes exemplary methods andsystems and is incorporated by reference in its entirety.

U.S. patent application Ser. No. 11/864,366, entitled “Time-BasedControl of a System having Integration Response,” inventor John L.Melanson, and filed on Sep. 28, 2007 describes exemplary methods andsystems and is incorporated by reference in its entirety. Referred toherein as Melanson III.

U.S. patent application Ser. No. 11/967,269, entitled “Power ControlSystem Using a Nonlinear Delta-Sigma Modulator with Nonlinear PowerConversion Process Modeling,” inventor John L. Melanson, and filed onDec. 31, 2007 describes exemplary methods and systems and isincorporated by reference in its entirety. Referred to herein asMelanson IV.

U.S. patent application Ser. No. 11/967,271, entitled “Power FactorCorrection Controller with Feedback Reduction,” inventor John L.Melanson, and filed on Dec. 31, 2007 describes exemplary methods andsystems and is incorporated by reference in its entirety. Referred toherein as Melanson V.

U.S. patent application Ser. No. 11/967,273, entitled “System and Methodwith Inductor Flyback Detection Using Switch Date Charge CharacteristicDetection,” inventor John L. Melanson, and filed on Dec. 31, 2007describes exemplary methods and systems and is incorporated by referencein its entirety. Referred to herein as Melanson VI.

U.S. patent application Ser. No. 11/967,275, entitled “ProgrammablePower Control System,” inventor John L. Melanson, and filed on Dec. 31,2007 describes exemplary methods and systems and is incorporated byreference in its entirety. Referred to herein as Melanson VII.

U.S. patent application Ser. No. 11/967,272, entitled “Power FactorCorrection Controller With Switch Node Feedback”, inventor John L.Melanson, and filed on Dec. 31, 2007 describes exemplary methods andsystems and is incorporated by reference in its entirety. Referred toherein as Melanson VIII.

U.S. patent application Ser. No. 12/047,269, entitled “Lighting Systemwith Power Factor Correction Control Data Determined from a PhaseModulated Signal,” inventor John L. Melanson, and filed on Mar. 12, 2008describes exemplary methods and systems and is incorporated by referencein its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to the field of electronics andlighting, and more specifically to a system and method to controllingand/or providing power to current regulated light sources, such as lightemitting diode light sources.

2. Description of the Related Art

Commercially practical incandescent light bulbs have been available forover 100 years. However, other light sources show promise ascommercially viable alternatives to the incandescent light bulb. LEDsare becoming particularly attractive as main stream light sources inpart because of energy savings through high efficiency light output,long life, and environmental incentives such as the reduction ofmercury.

LEDs are semiconductor devices and are driven by direct current. Thebrightness of the LED varies in direct proportion to the current flowingthrough the LED. Thus, increasing current supplied to an LED increasesthe brightness of the LED and decreasing current supplied to the LEDdims the LED.

FIG. 1 depicts a switching light emitting diode (LED) driver system 100.The LED driver system 100 includes a continuous current mode, buck-basedpower converter 102 to provide a constant mains voltage V_(mains) toswitching LED system 104. Voltage source 101 supplies an alternatingcurrent (AC) input mains voltage V_(mains) to a full, diode bridgerectifier 103. The voltage source 101 is, for example, a public utility,and the AC mains voltage V_(mains) is, for example, a 60 Hz/120 V mainsvoltage in the United States of America or a 50 Hz/230 V mains voltagein Europe. The rectifier 103 rectifies the input mains voltageV_(mains). The hold-up capacitor C1 holds an approximately directcurrent (DC) supply voltage V_(C1) across capacitor C1 relative to areference voltage V_(R). Supply voltage V_(C1) is also the outputvoltage of power converter 102 and the input voltage for controller 106.Input filter capacitor C2 provides a high pass filter for high frequencycomponents of the output voltage of rectifier 103. A thermistor NTC1provides in-rush current protection for power converter 102.

The controller 106 is, for example, a Supertex HV9910B integratedcircuit controller available from Supertex, Inc. of Sunnyvale, Calif.The supply voltage V_(C1) can vary from, for example, 8V to 450V.Controller 106 incorporates an internal voltage regulator to operatedirectly from the DC supply voltage V_(C). The controller 106 provides agate drive signal from the GATE output node to the n-channel metal oxidesemiconductor field effect transistor (MOSFET) Q1. Controller 106modulates the gate drive signal and, thus, the conductivity of MOSFET Q1to provide a constant current to switching LED system 104. Controller106 modifies the average resistance of MOSFET Q1 by varying a duty cycleof a pulse width modulated gate drive signal V_(GATE). Resistor R₁ andcapacitor C₃ provide external connections for controller 106 to theground reference.

Controller 106 generates and uses feedback to maintain a constantcurrent i_(LED). Controller 106 receives a current feedback signalV_(fb) representing a feedback voltage V_(fb) sensed across senseresistor R₂. The feedback voltage V_(fb) is directly proportional to theLED current i_(LED) in LEDs 108. If the feedback voltage V_(fb) exceedsa predetermined reference corresponding to a desired LED current, thecontroller 106 responds to the feedback voltage V_(fb) by decreasing theduty cycle of gate drive signal GATE to increase the average resistanceof MOSFET Q1 over time. If the feedback voltage V_(fb) is less than apredetermined reference corresponding to the desired LED current, thecontroller 106 responds to the feedback voltage V_(fb) by increasing theduty cycle of gate drive signal V_(GATE) to decrease the averageresistance of MOSFET Q1 over time.

The switching LED system 104 includes a chain of one or more, seriallyconnected LEDs 108. When the MOSFET Q1 is “on”, i.e. conductive, diodeD1 is reversed bias and, current i_(LED) flows through the LEDs andcharges inductor L₁. When the MOSFET Q1 is “off”, i.e. nonconductive,the voltage across inductor L₁ changes polarity, and diode D₁ creates acurrent path for the LED current i_(LED). The inductor L₁ is chosen soas to store enough energy to maintain a constant current i_(LED) whenMOSFET Q1 is “off”.

FIG. 2 depicts a power control system 200, which includes a switchingpower converter 202. The rectifier 103 rectifies the input mains voltageV_(mains) and supplies a rectified, time-varying, primary supply voltageV_(x) to the switching power converter. The switching power converter202 provides a power factor corrected, approximately constant voltagepower to load 222.

PFC and output voltage controller 214 controls PFC switch 208 so as toprovide power factor correction and regulate the output voltage V_(c) ofswitching power converter 202. The goal of power factor correctiontechnology is to make the switching power converter 202 appear resistiveto the voltage source 101. Thus, the PFC and output voltage controller214 attempts to control the inductor current i_(L) so that the averageinductor current i_(L) is linearly and directly related to the primarysupply voltage V_(x). The PFC and output voltage controller 214 suppliesa pulse width modulated (PWM) control signal CS₀ to control theconductivity of switch 208. In at least one embodiment, switch 208 is afield effect transistor (FET), and control signal CS₀ is the gatevoltage of switch 208. The values of the pulse width and duty cycle ofcontrol signal CS_(o) depend on two feedback signals, namely, theprimary supply voltage V_(x) and the capacitor voltage/output voltageV_(c). Output voltage V_(c) is also commonly referred to as a “linkvoltage”.

To convert the input voltage V_(x) into a power factor corrected outputvoltage V_(c), PFC and output voltage controller 214 modulates theconductivity of PFC switch 208. To regulate the amount of energytransferred and maintain a power factor close to one, PFC and outputvoltage controller 214 varies the period of control signal CS₀ so thatthe input current i_(L) tracks the changes in input voltage V_(x) andholds the output voltage V_(C) constant. Thus, as the input voltageV_(x) increases, PFC and output voltage controller 214 increases theperiod TT of control signal CS₀, and as the input voltage V_(x)decreases, PFC and output voltage controller 214 decreases the period ofcontrol signal CS₀. At the same time, the pulse width (PW) of controlsignal CS₀ is adjusted to maintain a constant duty cycle of controlsignal CS₀, and, thus, hold the output voltage V_(C) constant. Theinductor current i_(L) ramps ‘up’ when the switch 208 conducts, i.e. is“ON”. The inductor current i_(L) ramps down when switch 208 isnonconductive, i.e. is “OFF”, and supplies inductor current i_(L) torecharge capacitor 206. The time period during which inductor currenti_(L) ramps down is commonly referred to as the “inductor flyback time”.Diode 211 prevents reverse current flow into inductor 210. Inductorcurrent i_(L) is proportionate to the ‘on-time’ of switch 208. In atleast one embodiment, the switching power converter 202 operates indiscontinuous current mode, i.e. the inductor current i_(L) ramp up timeplus the inductor flyback time is less than the period of the controlsignal CS₀, which controls the conductivity of switch 208. Prodić,Compensator Design and Stability Assessment for Fast Voltage Loops ofPower Factor Correction Rectifiers, IEEE Transactions on PowerElectronics, Vol. 22, No. 5, Sep. 2007, pp. 1719-1729 (referred toherein as “Prodić”), describes an example of PFC and output voltagecontroller 214.

In at least one embodiment, the PFC and output voltage controller 214updates the control signal CS₀ at a frequency much greater than thefrequency of input voltage V_(x). The frequency of input voltage V_(x)is generally 50-60 Hz. The frequency 1/TT of control signal CS₀ is, forexample, between 20 kHz and 130 kHz. Frequencies at or above 20 kHzavoid audio frequencies and frequencies at or below 130 kHz avoidssignificant switching inefficiencies while still maintaining a goodpower factor of, for example between 0.9 and 1, and an approximatelyconstant output voltage V_(C).

Capacitor 206 supplies stored energy to load 212 when diode 211 isreverse biased. The capacitor 206 is sufficiently large so as tomaintain a substantially constant output voltage V_(c), as establishedby a PFC and output voltage controller 214 (as discussed in more detailbelow). The output voltage V_(c) remains at a substantially constanttarget value during constant load conditions. However, as loadconditions change, the output voltage V_(c) changes. The PFC and outputvoltage controller 214 responds to the changes in voltage V_(c) byadjusting the control signal CS₀ to return the output voltage V_(c) tothe target value. The PFC and output voltage controller 214 includes asmall capacitor 215 to filter any high frequency signals from theprimary supply voltage V_(x).

PFC and output voltage controller 214 controls the process of switchingpower converter 202 so that a desired amount of energy is transferred tocapacitor 206. The desired amount of energy depends upon the voltage andcurrent requirements of load 212. To determine the amount of energydemand of load 212, the PFC and output voltage controller 214 includes acompensator 228. Compensator 228 determines a difference between areference voltage V_(REF), which indicates a target voltage for outputvoltage V_(c), and the actual output voltage V_(c) sensed from node 222and received as feedback from voltage loop 218. The compensator 228generally utilizes technology, such as proportional integral (PI) typecontrol, to respond to differences in the output voltage V_(c) relativeto the reference voltage V_(REF). The PI control processes the error sothat the PFC and output voltage controller 214 smoothly adjusts theoutput voltage V_(c) to avoid causing rapid fluctuations in the outputvoltage V_(c) in response to small error signals. The compensator 228provides an output signal to the pulse width modulator (PWM) 230 tocause the PWM 230 to generate a control signal CS₀ that drives switch208.

An LED lighting system controller, such as controller 106, using asupply voltage that can vary from, for example, 8V to 450V generallyrequires a more expensive integrated circuit relative to an integratedcircuit designed to operate at a fraction of the maximum supply voltage.Using a conventional PFC controller with feedback control, when thepower demand of a load quickly decreases, the output voltage V_(C) willmomentarily increase while the PFC controller responds to output voltagefeedback by lowering the output voltage. Conventional switching powerconverters using compensators generally respond relatively slowly tolarge changes in load power demand. Additionally, conventional PFCcontrollers often include large and relatively expensive electrolyticcapacitors to accommodate voltage spikes.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a light emitting diode (LED)lighting system includes a power factor correction (PFC) and LED drivecontroller. The controller includes a digital signal processor, coupledto the LED feedback node and configured to: operate from a digital levelsupply voltage; generate a PFC control signal; and generate an LEDcurrent control signal. The controller further includes a first buffer,coupled to the processor, and configured to: operate from a medium levelsupply voltage. The medium level supply voltage is greater than thedigital level supply voltage. The controller is further configured toreceive the PFC control signal and convert the PFC control signal into aPFC switch control signal to control conductivity of a high voltage PFCswitch. The controller further includes a second buffer, coupled to theprocessor, and configured to: operate from the medium level supplyvoltage; receive the LED current control signal; and convert the LEDcurrent control signal into an LED current control switch signal tocontrol conductivity of a high voltage LED current control switch.

In another embodiment of the present invention, a method includesoperating a digital signal processor of a power factor correction (PFC)and output voltage controller from a digital level supply voltage andgenerating a PFC control signal; and generating an LED current controlsignal. The method further includes operating a first buffer, coupled tothe processor, from a medium level supply voltage. The medium levelsupply voltage is greater than the digital level supply voltage;receiving the PFC control signal. The method also includes convertingthe PFC control signal into a PFC switch control signal to controlconductivity of a high voltage PFC switch and operating a second buffer,coupled to the processor, from the medium level supply voltage. Themethod further includes receiving the LED current control signal andconverting the LED current control signal into an LED current controlswitch signal to control conductivity of a high voltage LED currentcontrol switch.

In a further embodiment of the present invention, a light emitting diode(LED) lighting system includes an LED lighting power system. Duringnormal operation of the LED lighting system the LED lighting powersystem generates a first source voltage relative to a common voltage.The first source voltage is a link voltage. The LED lighting powersystem includes a switching power supply having a power factorcorrection (PFC) switch, wherein during normal operation of the LEDlighting system, the PFC switch of the LED lighting power systemoperates at a current node voltage less than or equal to 0.1 times thefirst source voltage relative to the common voltage reference. The LEDlighting power system also includes an LED current control switch,wherein during normal operation of the LED lighting system, the LEDcurrent control switch operates at a current node voltage less than orequal to 0.1 times the first source voltage relative to the commonvoltage reference. The LED lighting system further includes a PFC andoutput voltage controller coupled to conductivity control nodes of thefirst and LED drive current switches. During normal operation of thelighting control system, the controller operates from a second sourcevoltage relative to the common voltage and controls conductivity of thePFC switch and the LED current control; and at least one LED coupled tothe LED current control switch.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features and advantages made apparent to those skilled in theart by referencing the accompanying drawings. The use of the samereference number throughout the several figures designates a like orsimilar element.

FIG. 1 (labeled prior art) depicts a switching light emitting diode(LED) driver system

FIG. 2 (labeled prior art) depicts a power control system, whichincludes a switching power converter.

FIG. 3 depicts a LED lighting system that includes a common referencenode at a common reference voltage.

FIG. 4 depicts a LED lighting system.

FIGS. 5A, 5B, 5C, and 5D depict various switches.

FIG. 5E depicts a driver circuit.

FIGS. 6A and 6B depict switching LED systems.

FIGS. 7-8 depict graphical relationships between various controlsignals, sense signals, and currents of the LED lighting system of FIG.4.

FIG. 9 depicts a spread spectrum system.

FIG. 10 depicts one embodiment of a feed forward lighting power andcontrol system.

FIG. 11 depicts a switching LED system with multiple current senseelements.

FIG. 12 depicts a switching LED system with a single current senseelement.

FIG. 13 depicts a graphical representation of non-overlapping controlsignals and current sense signals.

FIG. 14 depicts a graphical representation of overlapping controlsignals and current sense signals.

FIG. 15 depicts an embodiment of a controller of the lighting system ofFIG. 3.

DETAILED DESCRIPTION

A light emitting diode (LED) lighting system includes a PFC and outputvoltage controller and a LED lighting power system. The LED lightingpower system operates from a primary supply voltage derived from aprimary power supply. The controller operates from an auxiliary powersource supply, which provides an auxiliary voltage less than a linkvoltage generated by the LED lighting power system relative to a commonreference voltage at a common reference node. By utilizing a lowervoltage, in at least one embodiment, the controller can be manufacturedat a lower cost than a comparable controller supplied by the primarypower supply utilized by the LED lighting power system. Additionally,during normal operation of the LED lighting system, a power factorcorrection (PFC) switch and an LED drive current switch of the LEDlighting system, that respectively control power factor correction andLED drive current, are coupled to the common reference node and havecontrol node-to-common node, absolute voltage that allows the controllerto control the conductivity of the switches. In at least one embodiment,the PFC switch and the LED drive current switch each have a controlnode-to-common node, absolute voltage within 15% of the link voltagerelative to the common reference voltage. Having a current node voltagewithin 15% of the absolute value of the link voltage relative to thecommon reference voltage allows the controller to effectively controlthe switches.

In at least one embodiment, the controller 305 is manufactured in a12-20 Volt (“V”) complimentary metal oxide semiconductor (CMOS)integrated circuit process (“IC Process”), coupled to 200V-500V ratedfield effect transistors (FETs) external to the integrated circuit (IC)controller. This embodiment is a particularly cost-effective combinationof technologies. In a further refinement of the preferred embodiment,the IC Process also includes 5V or lower transistors in the ICcontroller in addition to the 12V-20V transistors, allowing for densedigital designs. A digital controller, in 0.35 micron or finer processtechnology allows for a very small, cost effective, digital controller.A 12V-20V process allows for the appropriate driving of the gates ofexternal high-voltage FETs. In at least one embodiment, the ICcontroller is controller 305 (FIGS. 3 and 4). The foregoing voltagelimits typically indicate that the high voltage devices (which haveapproximately 12V of gate-source voltage to be fully turned on, and lessthan 1V to be fully turned off) have sources at nearly the same voltagepotential, in order that the same controller can drive both.

An LED lighting system that includes dimming capability can be subjectto rapid changes in power demand by a switching LED system load. Theswitching LED system includes one or more light emitting diodes(LED(s)). For example, if the LED(s) are operating at full intensity anda dimming level of 15% of full intensity is requested, the power demandof the switching LED system is quickly and significantly reduced. In atleast one embodiment, the LED lighting system utilizes feedforwardcontrol to allow the controller to concurrently modify power demand bythe LED lighting power system and power demand of one or more switchingLED systems. Thus, in at least one embodiment, the LED lighting systemcan quickly respond to the lower power demand by reducing power receivedfrom a power source, such as a mains source, and use a compensator, suchas a proportional integral (PI) type control, to make relatively smallcorrections to maintain a desired LED lighting system output voltage.

Additionally, in at least one embodiment, the LED lighting systemincludes multiple switching LED systems, and each switching LED systemincludes at least one LED. In at least one embodiment, the LED lightingsystem utilizes a common current sense device to provide a commonfeedback signal to the controller representing current in at least twoof the switching LED systems. In at least one embodiment, utilizing acommon current sense device reduces a number of pins of the controllerused for feedback and reduces a number of current sense devices.

FIG. 3 depicts a LED lighting system 300 that includes a commonreference node 302 at a common reference voltage V_(com), such as aground reference during normal operation. The LED lighting system 300operates from two supply voltages, V_(x) and V_(AUX), which are bothreferenced to the common reference voltage. A third voltage, V_(D)(shown in FIG. 15), can be generated internal to the controller 305 andis preferably in the range of 1.5V-5.0V, depending on the chosen CMOStechnology. “Normal operation” refers to the operation of LED lightingsystem 300 after power has been supplied to the LED lighting system 300and any initial voltage or current transients have subsided. The LEDlighting system 300 generates a link voltage V_(C1). The PFC switch 308and LED drive current control switch 310 have absolute, controlnode-to-common node voltages within 15% of the difference between theabsolute link voltage V_(C1) minus the common reference voltage V_(com),ie. V_(C1)−V_(com). PFC and output voltage controller 305 (referred toas “controller 305”) operates from an auxiliary supply voltage V_(AUX).The absolute value of auxiliary supply voltage V_(AUX) is less than theabsolute value of the link voltage V_(C1).

FIGS. 5A, 5B, 5C, and 5D depict exemplary embodiments of switch 530,which represents one embodiment of switches 308 and 310. Referring toFIG. 5A, the nodes of 532, 534, and 536 of generic switch 530 representrespective control, common, and switching nodes. FIGS. 5B, 5C, and 5Drepresent embodiments of switch 530. Referring to FIG. 5B, switch 540 isan n-channel MOSFET, and gate node 542, source node 544, and drain node546 respectively represent a control node, a common node, and aswitching node. Referring to FIG. 5C, switch 550 is a bipolar junctiontransistor (BJT), and base node 552, emitter node 554, and collector 556respectively represent a control node, a common node, and a switchingnode. Referring to FIG. 5D, switch 560 is an insulated gate bipolartransistor (IGBT), and gate node 562, emitter node 564, and collector566 respectively represent a control node, a common node, and aswitching node.

FIG. 5E depicts an exemplary driver circuit 570, which represents oneembodiment of drivers 307 and 309. The source of p-channel FET 572 andthe drain of n-channel FET 574 are connected together and provide theoutput signal CS_(x) where CS_(x) represents control signals CS₁ andCS₂. The drain of p-channel FET 572 is connected to the high side supplyrail voltage, which is less than or equal to auxiliary voltage V_(AUX).The source of n-channel FET 574 is connected to the low side supply railvoltage V_(com). FETs 572 and 574 share a gate node 576 to receive thecontrol signal CS_(x).

Referring to FIG. 3, diode rectifier 103 rectifies the input mainsvoltage V_(mains) and supplies a rectified, time-varying, primary supplyvoltage V_(x) to a switching power converter 303. In at least oneembodiment, mains voltage V_(mains) is a mains voltage such as the mainsvoltage V_(mains) in FIGS. 1 and 2. Referring to FIG. 3, the auxiliarypower supply 311 provides low voltage power to the controller 305.Providing low voltage power to the controller 305 allows controller 305to be manufactured at a lower cost than higher voltage controllers.Additionally, during normal operation of the LED lighting system, apower factor correction (PFC) switch and an LED drive current switch ofthe LED lighting system, that respectively control power factorcorrection and LED drive current, are coupled to the common referencenode and have control node-to-common node, absolute voltage that allowsthe controller to control the conductivity of the switches. Duringnormal operation, the switching power converter 303 converts the primarysupply voltage V_(x) into an output, link voltage V_(C1). In at leastone embodiment, by referencing controller 305 to the common referencenode and establishing the control node-to-common node voltages ofswitches 308 and 310 within 15% of the voltage differenceV_(C1)−V_(com), controller 305 is able to control the conductivity ofthe switches 308 and 310 while operating from the auxiliary voltageV_(AUX) of auxiliary power supply 311. In at least one embodiment, thevoltages at current nodes 312 and 313 are within +1V of the commonreference voltage V_(com). A current sense resistor may or may not berequired in the PFC switch 308, depending on the control mode chosen forthe controller 305. In the preferred embodiment, controller 305 is adiscontinuous current mode controller and does not use a current sensefor controlling power factor correction.

The auxiliary power supply 311 supplies power to controller 305. Theauxiliary power supply 311 provides a supply voltage V_(AUX) less than,such as approximately from 1% to 15%, the absolute value of the linkvoltage V_(C1). For example, in at least one embodiment, the nominal RMSprimary supply voltage V_(x) is 110V, and the supply voltage V_(AUX) isany value within the range of +1V to +15V, such as +1V, +3V, +5V, +12V,or +15V. Because controller 305 is powered by a relatively small supplyvoltage, controller 305 can be manufactured less expensively than acontroller manufactured for higher supply voltages. The voltage V_(AUX)is chosen commensurate with the required drive voltage of the externalswitch. For an FET, this voltage is typically around 12V. For a bipolartransistor, current drive would often be used, and the voltage would be1V-2V.

During normal operation, the switching power converter 303 converts theprimary supply voltage V_(x) into an output, link voltage V_(C1). In atleast one embodiment, switching power converter 303 is a boostconverter, i.e. link voltage V_(C1)>V_(x). For a particular dimminglevel, the switching power converter 303 provides an approximatelyconstant current i_(LED) to LED light source 308. The current i_(LED)varies with dimming levels but, in at least one embodiment, isapproximately constant for a particular dimming level. The switchingpower converter 303 includes switch 308 to control the input currenti_(in) so that the average input current i_(in) is linearly and directlyrelated to the primary supply voltage V_(x), thereby making theswitching power converter 303 appear resistive to voltage source 301. Bycontrolling the input current i_(in), switch 308 also controls the valueof link voltage V_(C1). During normal operation of the LED lightingsystem 300, the link voltage V_(C1) has an approximately constant valueover time and, thus, approximates a DC voltage. In at least oneembodiment, the switching LED system 304 includes one or more individualLEDs or one or more parallel coupled strings of LED(s) as, for example,described in more detail with reference to FIGS. 5A and 5B. The linkvoltage V_(C1) is typically in the range of 200V-500V, depending on theAC mains voltage V_(mains).

Controller 305 generates PFC control signal CS₁ to control theconductivity of switch 308. Controller 305 includes a buffer 307 toprovide the drive current for PFC control signal CS₁. Controller 305generates a digital PFC control signal CS_(1D) that is amplified bybuffer 307 to generate PFC switch control signal CS₁. Buffer 307operates from a high side voltage supply rail of less than or equal toauxiliary voltage V_(AUX) and from a low side voltage supply rail ofcommon voltage V_(com). Controller 305 adjusts the pulse width of PFCcontrol signal CS₁ to increase as the primary supply voltage V_(x)increases and to decrease as primary supply voltage V_(x) decreases toprovide power factor correction. Controller 305 maintains a duty cycleof PFC control signal CS₁ while adjusting the pulse width of PFC controlsignal CS₁ to maintain an approximately constant link voltage V_(C1).Controller 305 receives feedback signal V_(x)′ to detect the value ofvoltage V_(x). Controller 305 also receives feedback signal V_(C1)′ todetect the value of voltage V_(C1). Controller 305 uses the value ofdetected feedback signals V_(x)′ and V_(C1)′ to adjust PFC controlsignal CS₁ so that switching power converter 303 provides power factorcorrection and maintains an approximately constant link voltage V_(C1).

The controller 305 can be implemented to generate the PFC control signalCS₁ in any of a variety of ways, such as the exemplary ways described inMelanson IV, Melanson V, and Melanson VII. The feedback signals V_(x)′and V_(C1)′ can be generated in any of a variety of ways, such as theexemplary ways described in Melanson V, Melanson VI, and Melanson VIII.

Controller 305 generates an LED current control switch signal CS₂ tomodulate the conductivity of LED drive current control switch 310.Controller 305 generates a digital LED current control signal CS_(2D)that is amplified by buffer 309 to generate LED current control switchcontrol signal CS₂. Controller 305 includes a buffer 309 to provide thedrive current for LED current control switch signal CS₂. Buffer 309operates from a high side voltage supply rail of less than or equal toauxiliary voltage V_(AUX) and from a low side voltage supply rail ofcommon voltage V_(com). In at least one embodiment, LED current controlswitch signal CS₂ is a duty cycle modulated gate drive signal. The dutycycle modulated gate drive signal modulating the conductivity of switch310 controls the LED current i_(LED) supplied by switching powerconverter 303. The current i_(LED) serves as the drive current forswitching LED system 304. Adjusting the current i_(LED) modifies theintensity of switching LED light system 304. The controller 305modulates the conductivity of switch 310 so that an average LED currenti_(LED) causes each LED in the switching LED system 304 to illuminate ata desired intensity level. In a non-dimmed configuration of LED lightingsystem 300, the desired intensity level is, for example, the full (100%)rated intensity of the LED(s) of the switching LED system 304 or zero(0) intensity (off).

As subsequently described in more detail, to regulate the LED drivecurrent i_(LED), the controller 305 receives a LED feedback signalLEDi_(sense) from a current sense device 314. In at least oneembodiment, the feedback signal LEDi_(sense) is the current i_(LED) or ascaled version of the current i_(LED). In another embodiment, thefeedback signal LEDi_(sense) is a voltage that is directly proportionalto the current i_(LED). The controller 305 responds to the feedbacksignal LEDi_(sense) by modifying the current delivered to the switchingLED system 304 to maintain a desired LED current i_(LED) and desiredlink voltage V_(C1). The current sense device 314 can be any devicecapable of sensing the LED current i_(LED). In at least one embodiment,current sense device 314 is a resistor, and the feedback signalLEDi_(sense) is a voltage sensed across the resistor. In at least oneembodiment, the feedback signal LEDi_(sense) is sensed by a magneticcurrent sensor in the proximity of current flowing through an inductor(such as inductor 606 of FIG. 6A or inductor 612 of FIG. 6B) inswitching LED system 304. In at least one embodiment, current sensedevice 314 is a current mirror circuit. Current mirrors are generallynot used in high voltage applications. Controller 305 can generate LEDcurrent control switch signal CS₂ in any of a variety of ways. MelansonIII describes an exemplary system and method for generating LED currentcontrol switch signal CS₂.

In at least one embodiment, LED lighting system 300 can dim the LED(s)of switching LED system 304, i.e. adjust the intensity of the LED(s) ofswitching LED system 304, in response to a dimmer signal D_(V). Thedimmer signal D_(V) can be a digital dimming signal D_(V) _(—)_(digital) or an analog dimming signal D_(V) _(—) _(analog) indicating adimming level for switching LED system 304. Values of dimmer signalD_(V) function as a target reference and are compared with LEDi_(sense)external to controller 305 or an integral part of an integrated circuitversion of controller 305. In at least one embodiment, the controller305 adjusts LED current control switch signal CS₂ to minimize adifference between the comparison between the dimmer signal D_(V) andthe feedback signal LEDi_(sense). In at least one embodiment, the dimmersignal D_(V) is generated and detected as described in Melanson I andMelanson II.

In at least one embodiment, the dimmer signal D_(V) represents a mappingof a conventional, duty cycle modified dimmer signal to predeterminedvalues different than the dimming level represented by the dimmer outputsignal value. In at least one embodiment, a conventional dimmer 320generates a dimming signal V_(DIM). The dimming signal V_(DIM) is, forexample, a duty cycle modified (i.e. phase-cut) analog signal whose dutycycle or phase angle represents a dimming level. Mapping system 322includes a lighting output function that converts the dimmer levelsindicated by dimming signal V_(DIM) to a digital dimming signal D_(V)_(—) _(digital) having values that map measured light levels toperception based light levels as described in conjunction with theexemplary systems and methods of Melanson I and Melanson II. In at leastone embodiment, controller 305 uses the digital dimming signal D_(V)_(—) _(digital) directly to generate LED current control switch signalCS₂. In at least one embodiment, digital-to-analog converter (DAC) 324converts the digital dimming signal D_(V) _(—) _(digital) into acorresponding analog dimming signal D_(V) _(—) _(analog). The digitaland analog versions of dimming signal D_(V) are generically referred tohere as dimming signal D_(V). Dimmer 320, mapping system 322, and DAC324 are shown in “dashed lines” because dimming is optional for LEDlighting system 300.

FIG. 4 depicts a LED lighting system 400, which represents oneembodiment of LED lighting system 300. LED lighting system 400 includesswitching power converter 402 to convert the rectified input voltageV_(x) into an approximately DC link voltage V_(C1). Switching powerconverter 402 and controller 305 also provide power factor correction.The switching power converter 402 includes a switch 308 that turns ‘on’(conducts) and turns ‘off’ (nonconductive) in response to a PFC controlsignal CS₁ generated by PFC and output voltage controller 305. Whenswitch 308 is ‘on’, inductor 408 energizes with the current I_(L1) fromthe full-bridge diode rectifier 103. When switch 308 is ‘off’, theinductor 408 drives current I_(L1) through diode 412 to charge capacitor408. The PFC control signal CS₁ varies the duty cycle of switch 308 sothat the DC voltage link voltage V_(C1) on storage capacitor 408averages to a desired value of DC voltage V_(C1). In at least oneembodiment, steady state voltage V_(C1) has an average value in therange of 200 V to 400 V. In at least one embodiment, current I_(L1)represents current i_(in) of FIG. 3. PFC and output voltage controller305 operates as previously described to control the duty cycle of switch308 such that current L_(i) is linearly proportional to the inputvoltage V_(x). Capacitor 432 provides filtering to smooth inductorcurrent I_(L1) so that the average inductor current I_(L1) is sinusoidin phase with input signal V_(x).

Controller 305 generates LED current control switch signal CS₂ based onthe value of the comparator 438 output signal V_(comp). In at least oneembodiment, comparator output signal V_(comp) is a voltage representinga logical “1” if the value of feedback signal LEDi_(sense) is greaterthan an analog value of dimmer signal D_(V) _(—) _(analog). Otherwise,the value of comparator output signal V_(comp) is a logical “0”. Thedimmer signal D_(V) is a target reference value, and controller 305generates controls signal CS₂ to modify the current i_(LED) to minimizedifferences between feedback signal LEDi_(sense) and dimmer signal D_(V)_(—) _(analog). The dimmer signal D_(V) _(—) _(analog) is scaled so thatwhen the difference between feedback signal LEDi_(sense) and dimmersignal D_(V) _(—) _(analog) is minimized, the intensity of the LED(s) ofswitching LED system 304 matches the dimming level indicated by dimmersignal D_(V) _(—) _(analog). As the dimming level indicated by dimmersignal D_(V) _(—) _(analog) changes, the value of comparator outputsignal V_(comp) also changes so that controller 305 causes LED currentcontrol switch signal CS₂ to track the changes in dimming levelindicated by dimmer signal D_(V) _(—) _(analog). As previouslydescribed, in at least one embodiment, controller 305 uses thecomparator output signal V_(comp) to generate LED current control switchsignal CS₂ as described in Melanson III.

FIGS. 6A and 6B depict exemplary embodiments of switching LED system304. Switching LED system 600 includes one or more LED(s) 602. TheLED(s) 602 can be any type of LED including white, amber, other colors,or any combination of LED colors. Additionally, the LED(s) 602 can beconfigured into any type of physical arrangement, such as linearly,circular, spiral, or any other physical arrangement. In at least oneembodiment, each of LED(s) 602 is serially connected. Capacitor 604 isconnected in parallel with LED(s) 602 and provides filtering to protectthe LED(s) 602 from AC signals. Inductor 606 smooths energy from LEDcurrent i_(LED) to maintain an approximately constant current i_(LED)when switch 310 conducts. Diode 608 allows continuing current flow whenswitch 310 opens.

In switching LED system 610, inductor 612 is connected in series withLED(s) 602 to provide energy storage and filtering. Inductor 612smoothes energy from LED current i_(LED) to maintain an approximatelyconstant current i_(LED) when switch 310 conducts. Diode 614 allowscontinuing current flow when switch 310 opens. Although two specificembodiments of switching LED system 304 have been described, switchingLED system 304 can be any switching LED system.

FIG. 7 depicts a graphical relationship 700 between the comparatorvoltage V_(COMP), LED current control switch signal CS₂, and currenti_(LEDsense) (FIG. 4). When LED current control switch signal CS₂ ishigh, switch 310 conducts, and LED current i_(LED) increases. When thecomparator voltage V_(COMP) goes high, PFC and output voltage controller305 keeps LED current control switch signal CS₂ high until thecomparator voltage V_(COMP) goes low again. In this manner, the averagecurrent i_(LEDsense), and, thus, the average LED current i_(LED), isresponsive to the dimmer signal Dv, and, thus, the intensity of theLED(s) in switching LED system are also responsive to dimmer signal Dv.

FIG. 8 depicts a graphical relationship 800 between LED current controlswitch signal CS₂ and current i_(LED). The LED current i_(LED) ramps upwhen LED current control switch signal CS₂ is high (i.e. causes switch310 to conduct) and ramps down when LED current control switch signalCS₂ is low (i.e. causes switch 310 to turn ‘off’). The average currenti_(LED) tracks the dimmer signal Dv. The intensity of switching LEDsystem 304 is approximately directly proportional to the driving LEDcurrent i_(LED).

FIG. 9 depicts one embodiment of a spread spectrum system 900. Thespread spectrum system can be included as part of controller 305 or canbe constructed using separate discrete components as a separate IC.Spread spectrum system 900 can also be implemented as code stored in acomputer readable medium and executable by controller 405. In general,spread spectrum system 900 receives an input signal T_(Target) andgenerates an output signal T_(OUT). Output signal T_(OUT) randomlyvaries from input signal T_(Target) within a predetermined range set byΔ_(max), and an average value of output signal T_(OUT) equals inputsignal T_(Target.) Input signal T_(Target) is, for example, a pulsewidth of control signals CS₁ and/or CS₂. The value of Δ_(max) is, forexample, +/−10% of a nominal value of PFC control signal CS₁. Multiplespread spectrum system 900 can be used by controller 305 to spread thespectrum of multiple input signals such as the pulse widths of controlsignals CS₁ and CS₂.

Spread spectrum system 900 includes a delta-sigma modulator 901.Delta-sigma modulator 901 includes an adder 902 that adds the currentvalue of input signal T_(Target) to a negative value of the previousvalue of output signal T_(OUT) to generate a difference signal T_(Diff).In at least one embodiment, spread spectrum system 900 is initialized asstartup with output signal T_(OUT)=0. The difference signal T_(DIff) isprocessed by loop filter 904 to generate a loop filter output signal U.

The values of delta-sigma modulator output signal T_(OUT) are randomizedaround the values of input signal T_(Target). A random number generator906 generates random output values of random signal RN that aremultipled by Δ_(max) to generate random signal RN′. During each cycle ofspread spectrum system 900, adder 910 adds the random signal RN′ to theloop filter output signal U, and quantizer 912 quantizes the sum of RN′and U to generate the quantization output signal T_(OUT). Random NumberGenerator 906 has predetermined value ranges set by a range limitingvalue Δ_(max). In at least one embodiment, RN′ varies approximately 10%.

Delta-sigma modulator 901 can be any delta-sigma modulator such as anyfirst order or multi-order delta-sigma modulator described in, forexample, Understanding Delta-Sigma Data Converters by Schreier andTemes, IEEE Press, 2005, ISBN 0-471-46585-2 or as available from CirrusLogic Inc. of Austin, Tex., U.S.A. The delta-sigma modulator 901provides noise-shaping and seeks to consistently generate values ofdelta-sigma output signal T_(OUT) that minimize the difference betweenoutput signal T_(OUT) and difference signal T_(Diff). Thus, delta-sigmamodulator 901 helps ensure that the average output signal T_(OUT) equalsthe average input signal T_(Target).

FIG. 10 depicts one embodiment of a feed forward lighting power andcontrol system 1000. Power and control system 1000 preferably alsoincludes a common reference node for switches 308 and 310 (throughcurrent sense device 314) and controller 1002. Controller 1002represents one embodiment of controller 305. Controller 1002 islogically divided into two separate control systems, PFC control system1004 to control power factor correction and regulate the link voltageV_(C1) of switching power converter 402, and switching LED systemcontroller 1006 to control the LED current i_(LED) and, thus, controlthe intensity (i.e. brightness) of switching LED system 304.

The power and control system 1000 utilizes feed forward control so thatPFC controller 1004 can more rapidly respond to changing power demandsof Switching LED system light source 304 due to dimming When dimmersignal Dv indicates a change in the dimming level of light source 304,switching LED system controller 1006 responds to dimming signal Dv bydecreasing the pulse width of duty cycle modulated LED current controlswitch signal CS₂ to reduce the average values of current i_(LED).Decreasing current i_(LED) reduces the power demand of light source 304.

Feed forward control allows PFC system controller 1004 to anticipatepower demand changes of light source 304 due to, for example, dimmingThe PFC system controller 1004 is configured to provide a specificoutput voltage link voltage V_(C1) for a specific dimming level. In atleast one embodiment, the controller 1004 responds to comparison signalV_(comp), which indicates a change in requested dimming level and, thus,a change in power demand by light source 304 by proportionately changingthe pulse width of LED current control switch signal CS₂. In at leastone embodiment, the dimmer signal Dv is provided directly to controller1004 as shown by the dashed line 1008. However, providing dimmer signalDv to controller 1004 may require an extra pin for controller 1002,which generally adds cost to controller 1002. Using feed forwardcontrol, the controller 1002 can concurrently modify power demand by thepower factor correction control system 1004 and modify power supplied bythe switching LED system controller 1006. The term “concurrently”includes short delays due to, for example, processing by controller1006.

In accordance with changes in a dimming level indicated by the dimmersignal D_(V), in at least one embodiment, the PFC system controller 1004includes a proportional integrator (PI) compensator 1010 that receives afeedback signal link voltage V_(C1) representing the link voltage V_(C1)and generates an output signal using a PI transfer function, such as thePI transfer function and system of Melanson IV. However, because thedimmer signal D_(V) anticipates power demand by light source 304, thePFC controller 1004 can concurrently respond to dimming level changesand, the PI compensator 1010, in at least one embodiment, only makespower demand adjustments of, for example, 10% of the total powerdelivered by the power and control system 1000. Responding more rapidlyto power demand changes in light source 304 allows switching powerconverter 402 to utilize a smaller capacitor value, such as 4.7 μF forcapacitor 408 because increases of link voltage V_(C1) are reduced towithin the operating characteristics of ceramic, polypropylene, andother capacitors that have advantageous properties relative toelectrolytic capacitors such as better temperature characteristicsbecause light source 304 tends to generate higher temperatures bettersuited for ceramic, polypropylene, and other higher temperaturecapacitors. In at least one embodiment, controller 1004 generates PFCcontrol signal CS₁ in the same manner as controller 305 so that thechanges in the dimming level indicated by dimmer signal D_(V) arecommensurate with changes to the power (V_(C1)·i_(in)) delivered byswitching power converter 402 while maintaining an approximatelyconstant link voltage V_(C1).

FIG. 11 depicts a switching light source bank 1100 having N+1 switchingLED systems, where N is an integer greater than or equal to 1. SwitchingLED system bank 1100 is a substitution for switching LED system 304. Inat least one embodiment, each light source 304.x is a light source suchas switching LED system 304, where x denotes the x^(th) light source andis, for example, an integer and a member of the set {0, . . . , N}. Eachof the N+1 light sources includes at least one LED and the number andcolor of each LED for each light source is a matter of design choice.Each light source 304.x is connected to a respective switch 1104.x, andeach switch 1104.x is an n-channel FET. In at least one embodiment,controller 305 independently controls each light source 304.x bygenerating respective control signals CS₂.0, . . . , CS₂.N to controlthe conductivity of switches 1104.0, . . . , 1104N. The average valuesof the drive currents i_(LED).0, . . . , i_(LED).N control therespective intensity of LED(s) of switching LED systems 304.0, . . . ,304.N. Switching LED systems 304.0, . . . , 304.N are connected torespective current sense elements 314.0, . . . , 314.N.

The current sense elements 314.0, . . . , 314.N can be different oridentical. Each current sense element 314.x provides a feedback signalLEDsense.x to controller 305. In at least one embodiment, controller 305generates each control signal CS_(2x) in the same manner as thegeneration of LED current control switch signal CS₂ (FIG. 4). The outputsignals of LEDi_(sense).0, . . . , LEDi_(sense).N are fed back tocontroller 305 to allow controller 305 to adjust the switching frequencyof switches 1104.0, . . . , 1104.N and, thus, correlate LED drivecurrents i_(LED).0, . . . , i_(LED).N with a desired intensity of theLED(s) of light sources 304.0, . . . , 304.N. In at least oneembodiment, the desired intensity is a dimming level indicated by dimmersignal D_(V). The type, number, and arrangement of LED(s) in switchingLED systems 304.0, . . . , 304.N is a matter of design choice anddepends, for example, on the range of desired intensity and colortemperatures of switching LED systems 304.0, . . . , 304.N.

FIG. 12 depicts a switching LED system bank 1200, which represents asubstitution for switching LED system 304 (FIG. 4). One current senseelement 312 provides a feedback signal LEDi_(sense) that represents theLED sense currents of all switching LED systems 304.0, . . . , 304.N tosense each of the LED sense currents i_(LEDsense).0, . . . ,i_(LEDsense).N for respective switching LED systems 304.0, . . . ,304.N. Each of the switches 1204.0, . . . , 1204.N have a common currentnode 1206. At the common current node 1206, all of the LED sensecurrents i_(LEDsence).0, . . . , i_(LEDsense).N are combined, and thefeedback signal LEDi_(sense) from current sense device 312 representsthe combination of all of the LED sense currents i_(LEDsense).0, . . . ,i_(LEDsense).N. In at least one embodiment, feedback signalLEDi_(sense)=1/x·(i_(LEDsense).0+i_(LEDsense).1+, . . . ,+i_(LEDsense).N), where “x” is a scaling factor of current sense device312. Utilizing a common sense element 312 reduces a number of pins foran integrated circuit implementation of controller 1208, which reducesthe cost of controller 1208. Controller 1208 represents one embodimentof controller 305.

FIG. 13 depicts a graphical representation 1300 of non-overlappingcontrol signals and current sense signals. The operation of LED sourcebank 1200 and controller 1208 (FIG. 12) are described in conduction withthe signals of FIG. 13. Control signals CS₂.0 and CS₂.N represent twoexemplary control signals for control signals CS₂.0, . . . , CS₂.N.Control signals CS₂.0 and CS₂.N are depicted with a duty cycle of 0.25,i.e. pulse width/period, and non-overlapping pulse widths. During eachpulse of control signals CS₂.0 and CS₂.N, respective currentsi_(LEDsense.) 0 and i_(LEDsense).N flow through respective switches1204.0 and 1204.N and are combined into the single LEDi_(sense) feedbacksignal from current sense device 312.

Referring to FIGS. 12 and 13, controller 1208 includes an LED currentdetector 1210 that detects and determines the individual LED currentsi_(LED) in switching LED systems 304.0, . . . , 304.N from theLEDi_(sense) feedback signal. The location in time of each contributionof currents i_(LEDsense).0 and i_(LEDsense).N in the feedback signalLEDi_(sense) corresponds to the respective pulses of controls signalsCS₂.0 and CS₂.N.

In at least one embodiment, in a dimmable configuration, dimmer signalD_(V) is used to indicate a dimming level for switching LED systems304.0, . . . , 304.N. Comparator 438 compares the LEDi_(Sense) feedbacksignal to the dimmer signal D_(V). Variations in the comparator outputsignal V_(comp) occur at approximately the same time as the contributionof currents i_(LEDsense).0 and i_(LEDsence).N to the feedback signalLEDi_(sense). Since controller 1208 generates control signals CS₂.0 andCS₂.N, the times at which currents i_(LEDsense).0 and i_(LEDsense).Nwill vary the comparator output signal V_(comp) are also known by LEDcurrent detector 1210. By knowing which changes in comparator outputsignal V_(comp) correspond to each particular current of switching LEDsystems 304.0, . . . , 304.N, controller 1208 can adjust each LEDcurrent control switch signal CS₂.0 and CS₂.N in response to the dimmersignal D_(V) to dim the LEDs of switching LED systems 304.0 and 304.N tothe dimming level indicated by dimmer signal D_(V). In at least oneembodiment, controller 1208 generates each LED current control switchsignal CS₂.0, . . . , CS₂.N in any manner described in conjunction withcontroller 305.

In at least one embodiment, the switching LED systems 304.0, . . . ,304.N are not dimmed In this embodiment, LED current detector 1210receives the feedback signal LEDi_(sense) directly. Since controller1208 generates control signals CS₂.0 and CS₂.N, the times at whichcurrents i_(LEDsense).0 and i_(LEDsense).N, LED current detector 1210detects the contribution of currents i_(LEDsense).0 and i_(LEDsense).Nduring any of the respective times during which respective controlsignals CS₂.0 and CS₂.N are non-overlapping.

FIG. 14 depicts a graphical representation 1400 of overlapping controlsignals and current sense signals for processing by controller 1208 togenerate multiple control signals for multiple light sources from asingle feedback signal LEDi_(sense). The overlapping control signalseach have a duty cycle of 0.5. LED current detector 1210 detects thecontributions of currents i_(LEDsense).0 and i_(LEDsense).N in feedbacksignal LEDi_(sense) or comparator output signal V_(comp) at times whenthe control signals CS₂.0 and CS₂.N are non-overlapping. For example,LED current detector 1210 detects the contribution of i_(LEDsense).0during times t₁ to t₂, t₅ to t₆, t₉ to t₁₀, and so on. Likewise, LEDcurrent detector detects the contribution of i_(LEDsense.)N during timest₃ to t₄, t₇ to t₈, and so on.

FIG. 15 depicts lighting system 1500, which is one embodiment oflighting system 300. Lighting system 1500 includes PFC switch 1502,which is an n-channel FET and represents one embodiment of switch 308.PFC switch 1502 operates between the primary supply voltage V_(x) andthe common reference voltage V_(com). PFC switch 1502 does not have tobe connected directly to the primary supply voltage V_(x). In at leastone embodiment, PFC switch 1502 is coupled through other components (notshown) to a primary supply voltage node 1506 conducting primary supplyvoltage V_(x). Lighting system 1500 also includes LED drive currentcontrol switch 1504, which is an n-channel FET and represents oneembodiment of switch 310. LED drive current control switch 1504 iscoupled through switching LED system 304 to link voltage node 1508. LEDdrive current control switch 1504 operates between the link voltageV_(x) and the common reference voltage V_(com). Voltages V_(x) andV_(C1) are both switching power converter voltages and are collectivelyreferred to as “high” supply voltages 1510 because they represent thehighest voltages in the lighting system 1500. Nodes 1506 and 1508 arereferred to as high voltage source nodes. PFC switch 1502 is, thus,referred to as a high voltage PFC switch, and LED current control switch1504 is, thus, referred to as a high voltage LED current control switch.In at least one embodiment, the root mean square (RMS) of high supplyvoltages 1510 is greater than or equal to 100 V.

The lighting system 1500 also includes PFC and output voltage controller1512, which in at least one embodiment is identical to controller 305.PFC and output voltage controller 1512 operates from at least twodifferent voltages, which are lower than the high voltages 1510. Outputbuffers 307 and 309 operate between voltages V_(B) and the commonreference voltage. Voltage V_(B) is less than or equal to auxiliaryvoltage V_(AUX) and greater than or equal the digital voltage referenceV_(D). The voltage V_(B) is set to be sufficient to drive the gates ofswitches 1502 and 1504 and, thus, control the conductivity of switches1502 and 1504. Voltage V_(B) is referred to as a “medium level” supplyvoltage. In at least one embodiment, the medium level supply voltage isin the range of 8 V to 50 V.

The lighting system 1500 also includes a digital signal processor (DSP)1514 to generate PFC control signal CS_(1D) and LED current controlsignal CS_(2D). The DSP 1514 is coupled to an LED feedback node 1518.DSP 1514 operates between a digital supply voltage V_(D) and the commonreference voltage V_(com). The digital supply voltage V_(D) issufficient to operate the digital components of DSP 1504 and is, forexample, in the range of 3 V to 8 V. A level shifter (LS) 1516 levelshifts the digital PFC control signal CS_(1D) and digital LED currentcontrol signal CS_(2D) from DSP 1504 to a level sufficient to controlthe conductivity of respective buffers 307 and 309. The digital supplyvoltage V_(D) can be a stepped down version of the auxiliary voltageV_(AUX) generated internally by controller 1512.

Thus, although the controller 1512 operates from a digital voltageV_(D), and an auxiliary voltage V_(AUX) and the switches operates fromhigh voltages 1510, the lighting system 1500 has a common referencevoltage V_(com) to allow all the components of lighting system 1500 towork together. By operating from auxiliary voltage V_(AUX), thecontroller 1512 can be fabricated using lower cost fabricationtechniques than a controller operating from the high voltages 1510.

Thus, in at least one embodiment, a LED lighting system controlleroperates from a supply voltage V_(AUX) less than a link voltage V_(C1)generated by the LED lighting power system relative to a commonreference voltage at a common reference node. By utilizing a lowervoltage, in at least one embodiment, the controller can be manufacturedat a lower cost than a comparable controller supplied by the primarypower supply utilized by the LED lighting power system. Additionally,during normal operation of the LED lighting system, a power factorcorrection (PFC) switch and an LED drive current switch of the LEDlighting system, that respectively control power factor correction andLED drive current, are coupled to the common reference node and havecontrol node-to-common node, absolute voltage that allows the controllerto control the conductivity of the switches. In at least one embodiment,the PFC switch and the LED drive current switch each have a controlnode-to-common node, absolute voltage within 15% of an absolute value ofthe link voltage relative to the common reference voltage. In at leastone embodiment, the LED lighting system utilizes feed forward control toconcurrently modify power demand by the LED lighting power system andpower demand of one or more switching LED systems. In at least oneembodiment, the LED lighting system utilizes a common current sensedevice to provide a common feedback signal to the controllerrepresenting current in at least two of the switching LED systems.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions and alterations can bemade hereto without departing from the spirit and scope of the inventionas defined by the appended claims.

What is claimed is:
 1. An apparatus comprising: a power factorcorrection (PFC) and light emitting diode (LED) drive controller, thecontroller comprising: a signal processor, coupled to the LED feedbacknode and configured to: operate from a first level supply voltage;generate a PFC control signal; and generate an LED current controlsignal; a first buffer, coupled to the processor, and configured to:operate from a second level supply voltage, wherein the second levelsupply voltage is greater than the first level supply voltage; receivethe PFC control signal; and convert the PFC control signal into a PFCswitch control signal to control conductivity of a PFC switch; and asecond buffer, coupled to the processor, and configured to: operate fromthe second level supply voltage; receive the LED current control signal;and convert the LED current control signal into an LED current controlswitch signal to control conductivity of an LED current control switch.2. The apparatus of claim 1 wherein the first level supply voltage is adigital level supply voltage.
 3. The apparatus of claim 1 wherein thecontroller is configured to generate multiple control signals torespectively control multiple switching LED systems.
 4. The apparatus ofclaim 1 wherein the controller is configured to internally generate thefirst level supply voltage from the second level supply voltage.
 5. Theapparatus of claim 1 further comprising a plurality of LEDs, wherein,during operation of the controller, the LED current control switchcontrols current through the plurality of LEDs.
 6. The apparatus ofclaim 1 wherein the PFC switch is a high voltage PFC switch, and the LEDcurrent control switch is a high voltage LED current control switch. 7.The apparatus of claim 1 wherein the controller is an integratedcircuit, and the signal processor comprises a digital signal processor.8. The apparatus of claim 1 wherein the controller includes at least oneinput to receive a dimming signal representing a dimming level from adimmer and wherein the second buffer is further configured to: convertthe LED current control signal into an LED current control signal tocontrol one or more LEDs in accordance with the dimming level from thedimmer.
 9. The apparatus of claim 8 wherein the dimming signalrepresenting the dimming level represents a mapping of a signalgenerated by the dimmer to a predetermined value different than thedimming level from the dimmer.
 10. The apparatus of claim 8 wherein oneor more of the switching LED systems includes multiple LEDs.
 11. Theapparatus of claim 1 further comprising: a switching power convertercoupled to the PFC and LED drive controller; a primary power supply,coupled to the signal processor, to supply a primary supply voltage tothe switching power converter; and an auxiliary power supply, coupled tothe controller, to supply the first level supply voltage to thecontroller, wherein the first level supply voltage is less than theprimary supply voltage.
 12. The apparatus of claim 11 wherein the firstlevel supply voltage comprises a voltage generated from the medium levelsupply voltage.
 13. The apparatus of claim 1 further comprising: adimmer coupled to the controller, wherein the dimmer is configured togenerate a dimmer signal representing a dimming level and the controlleris configured to receive a signal representing the dimming level. 14.The apparatus of claim 13 wherein the first level supply voltage is astepped down version of the second level supply voltage, and thecontroller is configured to internally generate the first level supplyvoltage from the second level supply voltage.
 15. A method comprising:operating a signal processor of a power factor correction (PFC) andoutput voltage controller from a first level supply voltage; generatinga PFC control signal; and generating an LED current control signal;operating a first buffer, coupled to the processor, from a second levelsupply voltage, wherein the second level supply voltage is greater thanthe first level supply voltage; receiving the PFC control signal;converting the PFC control signal into a PFC switch control signal tocontrol conductivity of a PFC switch; and operating a second buffer,coupled to the processor, from the second level supply voltage;receiving the LED current control signal; and converting the LED currentcontrol signal into an LED current control switch signal to controlconductivity of an LED current control switch.
 16. The method of claim15 wherein the first level supply voltage is a digital level supplyvoltage.
 17. The method of claim of 15 further comprising: generatingthe first level supply voltage from the second level supply voltageinternally by the controller.
 18. The method of claim 15 furthercomprising: controlling current in a plurality of LEDs.
 19. The methodof claim 15 wherein the PFC switch is a high voltage PFC switch, and theLED current control switch is a high voltage LED current control switch.20. The method of claim 15 wherein the controller includes an LEDfeedback node to receive an LED current feedback signal representing oneor more current levels in one or more switching LED systems and avoltage feedback node to receive an input voltage feedback signalrepresenting an input voltage level provided to a lighting system thatincludes the controller, the method further comprising: generating thePFC control signal in response to the input voltage level represented bythe input voltage feedback signal; and generating the LED drive currentcontrol signal in response to the one or more current levels representedby the LED current feedback signal.
 21. The method of claim 15 whereinthe first supply voltage has an absolute value less than or equal to 8volts, the second level supply voltage has an absolute value less thanor equal to 50 volts, and the high voltage PFC switch is coupled betweenvoltage nodes having a voltage difference during normal operation of alighting system that includes the controller of at least 100 volts, andthe high voltage LED drive current switch is coupled between voltagenodes having a voltage difference during normal operation of thelighting system of at least 100 volts.
 22. The method of claim 15further comprising: supplying a primary supply voltage to a switchingpower converter; and supplying the first level supply voltage to thecontroller, wherein the first level supply voltage is less than theprimary supply voltage.
 23. The method of claim 22 wherein the firstlevel supply voltage comprises a voltage generated from the medium levelsupply voltage.
 24. The method of claim 15 further comprising:generating multiple control signals to respectively control multipleswitching LED systems.
 25. The method of claim 24 wherein one or more ofthe switching LED systems includes multiple LEDs.
 26. The method ofclaim 15 further comprising: generating the first level supply voltagefrom the second level supply voltage.
 27. The method of claim of 26wherein generating the first level supply voltage from the second levelsupply voltage comprises: stepping down the second level supply voltageinternally by the controller to generate the first level supply voltage.28. The method of claim 15 further comprising: receiving a dimmingsignal representing a dimming level from a dimmer; and dimming one ormore LEDs in accordance with the dimming level.
 29. The method of claim28 further comprising: mapping a dimmer signal generated by a dimmer toa predetermined value different than the dimming level from the dimmerto generate the dimming signal.
 30. The method of claim 28 whereindimming one or more LEDs in accordance with the dimming level comprises:operating the second buffer to convert the LED current control signalinto an LED current control signal to control one or more LEDs inaccordance with the dimming level from the dimmer.
 31. The method ofclaim 28 further comprising: generating a dimmer signal representing thedimming level.
 32. The method of claim 15 further comprising: generatinga first voltage, wherein the first voltage is a link voltage; operatinga switching power converter of an LED lighting power system from thefirst source voltage relative to a common voltage, wherein the switchingpower converter includes the PFC switch; operating the PFC switch at acontrol node-to-common node, absolute voltage to allow the PFC andoutput voltage controller to control the PFC switch and provide powerfactor correction for the switching power converter; operating the LEDcurrent control switch at a control node-to-common node, absolutevoltage to allow the PFC and output voltage controller to control theLED current control switch to supply an approximately constant currentto an LED switching system for each dimming level indicated by a dimmersignal; and controlling conductivity of the PFC switch and the LEDcurrent control switch with the PFC and output voltage controller. 33.The method of claim 32 wherein: operating the PFC switch of theswitching power converter at a control node-to-common node, absolutevoltage to allow a PFC and output voltage controller to control the PFCswitch and provide power factor correction for the switching powerconverter comprises operating the PFC switch of the LED lighting powersystem at a control node-to-common node, absolute voltage less than orequal to 0.15 times the first source voltage relative to the commonvoltage reference; and operating the LED current control switch at acontrol node-to-common node, absolute voltage to allow the PFC andoutput voltage controller to control the LED current control switch tosupply an approximately constant current to an LED switching system foreach dimming level indicated by a dimmer signal comprises operating theLED current control switch at a control node-to-common node, absolutevoltage less than or equal to 0.15 times the first source voltagerelative to the common voltage reference.
 34. The method of claim 32wherein the PFC and LED current control switches comprise field effecttransistors and controlling conductivity of the PFC switch and LEDcurrent control switch with the PFC and output voltage controllercomprises providing respective duty cycle modified control signals togates of the PFC switch and LED current control switch.
 35. The methodof claim 32 further comprising: receiving a rectified primary supplyvoltage, wherein a root mean square (RMS) value of the primary supplyvoltage is greater than the second level voltage; boosting the primarysupply voltage to the first source voltage, wherein boosting the primarysupply voltage further comprises modulating the conductivity of the PFCswitch to generate a power factor corrected first source voltage. 36.The method of claim 32 further comprising: receiving a dimmer signal;and controlling conductivity of the PFC switch and the LED currentcontrol switch further comprises: concurrently controlling theconductivity of the PFC switch and the LED current control switch tomodify power demand by LED lighting power system and modify powersupplied by a lighting system coupled to the controller in accordancewith changes in a dimming level indicated by the dimmer signal.
 37. Themethod of claim 32 wherein the second source voltage is less than orequal to approximately 15% of the first source voltage.
 38. The methodof claim 32 further comprising: operating one or more transistors of thePFC and output voltage controller from a third voltage source node andthe common voltage reference, wherein the third voltage is lower thanthe link voltage and the second source voltage.
 39. The method of claim32 wherein a switching LED system includes the LED and controllingconductivity of the LED current control switch further comprises:receiving a feedback signal from a switching LED system; and respondingto the feedback signal to maintain a predetermined current to each LED.40. The method of claim 39 further comprising: sensing a voltage acrossa resistor representing a current through each LED, wherein the voltagesensed across the resistor is the feedback signal.
 41. The method ofclaim 32 further comprising: operating additional LED current controlswitches at respective current node voltages less than or equal to 0.15times the first source voltage relative to the common voltage reference,wherein each LED current control switch controls current through arespective chain of LEDs and each chain of LEDs includes at least oneLED; receiving a single feedback signal representing current conductedby each LED current control switch; and controlling conductivity of eachLED current control switch with the PFC and output voltage controller inresponse to the feedback signal.
 42. The method of claim 41 whereincontrolling conductivity of each LED current control switch with the PFCand output voltage controller in response to the feedback signalcomprises: determining during separate periods of time the respectivecurrents conducted by each LED current control switch.
 43. The method ofclaim 32 further comprising: operating additional LED current controlswitches at respective current node voltages less than or equal to 0.15times the first source voltage relative to the common voltage reference,wherein each LED current control switch controls current through arespective chain of LEDs and each chain of LEDs includes at least oneLED; receiving feedback signals, wherein each feedback signal representsa respective current conducted by one of the LED current controlswitches; and controlling conductivity of each LED current controlswitch with the PFC and output voltage controller in response to thefeedback signal.
 44. A light emitting diode (LED) lighting systemcomprising: an LED lighting power system, wherein during normaloperation of the LED lighting system the LED lighting power systemgenerates a first source voltage relative to a common voltage reference,wherein the first source voltage is a link voltage, and the LED lightingpower system includes: an auxiliary power supply to supply an auxiliarysupply voltage; a switching power supply having a power factorcorrection (PFC) switch, wherein during normal operation of the LEDlighting system, the PFC switch of the LED lighting power systemoperates at a current node voltage less than or equal to 0.1 times thefirst source voltage relative to the common voltage reference; and anLED current control switch, wherein during normal operation of the LEDlighting system, the LED current control switch operates at a currentnode voltage less than or equal to 0.1 times the first source voltagerelative to the common voltage reference; a dimmer coupled to the LEDlighting power system to generate a dimming signal; a PFC and outputvoltage, integrated circuit controller coupled to conductivity controlnodes of the first and LED drive current switches and to the dimmer,wherein during normal operation of the lighting control system, thecontroller operates from the auxiliary supply voltage relative to thecommon voltage and controls conductivity of the PFC switch and the LEDcurrent control in accordance with the dimming signal; and at least oneLED coupled to the LED current control switch.